The present invention relates to a method for manufacturing an interphase insulating sheet of a rotating electric machine, and an electric compressor.
Japanese Unexamined Patent Application Publication No. 2009-77582 discloses an interphase insulating sheet (interphase insulating paper) of a rotating electric machine that is interposed between any two coil ends of U-, V-, and W-phase coils to insulate such coil ends from each other. The interphase insulating sheet disclosed in the above publication includes a pair of insulating portions that insulate coils of different phases from each other and a plurality of bridge pieces that is inserted in slots between adjacent teeth formed in a stator core and connects the pair of insulating portions to each other. Each of the insulating portions of a strip shape is formed in an annular shape by overlapping opposite ends thereof with each other and welding the overlapping portion by ultrasonic welding.
An ultrasonic welding apparatus used to weld the overlapping portion of each insulating portion includes a ferrous workbench and an ultrasonic horn. In the ultrasonic welding, the overlapping portion of the insulating portion is first placed on the upper surface of the workbench and then the ultrasonic horn is placed on the upper surface of the overlapping portion. The overlapping portion held between the workbench and the ultrasonic horn is ultrasonically welded.
The U-phase coil is passed through a first group of slots and the V-phase coil is passed through a second group of slots. At this time, the bridge pieces of the interphase insulating sheet insulating coil ends of the U-phase coil from coil ends of the V-phase coil are inserted in the second group of slots. By so doing, the pair of insulating portions interposed between the coil ends of the U-phase coil and the coil ends of the V-phase coil insulates the coil ends of the U-phase coil from the coil ends of the V-phase coil.
Subsequently, the W-phase coil is passed through a third group of slots. At this time, the bridge pieces of the interphase insulating sheet insulating the coil ends of the V-phase coil from coil ends of the W-phase coil are inserted in the third group of slots. With this configuration, the pair of insulating portions interposed between the coil ends of the V-phase coil and the coil ends of the W-phase coil insulate the coil ends of the V-phase coil from the coil ends of the W-phase coil.
The opposite ends of each insulating portion are overlapped with each other in the overlapping portion of the insulating portion. The overlapping portion is less flexible as compared with the remaining part of the insulating portion. In is other words, the insulating portion is harder to bend at the overlapping portion. For example, in the case that the insulating portion which insulates the coil ends of the U-phase coil from the coil ends of the V-phase coil is inserted through the third group of slots, the overlapping portion of the insulating portion, which is poor in flexibility, may interfere with the W-phase coil during the insertion of the W-phase coil in the third group of slots, thus hampering the insertion of the W-phase coil. For this reason, it is preferable that the distance of the overlapping portions in the extending direction of the insulating portions should be as small as possible.
The weld area in the overlapping portion in the extending direction of the insulating portion decreases with a decrease of the distance of the overlapping portion in the extending direction of the insulating portion. In order to increase the weld area, it may be contemplated to use an ultrasonic horn having a rectangular shape in a plan view and to place the ultrasonic horn on the upper surface of the overlapping portion so that the longitudinal direction of the bottom surface of the ultrasonic horn is oriented in the direction in which the bridge pieces extend.
However, in the ultrasonic welding process, the ultrasonic horn rotates on the overlapping portion of the insulating portion while applying ultrasonic vibration. The rotation of the ultrasonic horn on the overlapping portion may cause part of the edges of the overlapping portion at the opposite longitudinal ends thereof to be moved out of the overlapping portion. As a result, the area in the overlapping portion that is held between the workbench and the ultrasonic horn is reduced after ultrasonic vibration is applied to the ultrasonic horn, with the result that stable ultrasonic welding fails to be achieved and the welding strength in the overlapping portion is lowered.
The present invention, which has been made in view of the above circumstances, is directed to a method for manufacturing an interphase insulating sheet of a rotating electric machine that ensures welding strength in the overlapping portion of the insulating portion, and also to an electric compressor.